Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities and Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail)

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Marketable Securities and Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2020
Dec. 31, 2019
Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities $ 114,896 $ 125,505  
Cash and cash equivalents 33,410 85,451 $ 15,268
Marketable securities, current 82,816 39,633  
Marketable securities, non-current 2,000 1,510  
Cash Equivalents      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Cash and cash equivalents 30,080 84,362  
Money Market Funds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 27,080 79,970  
Commercial Paper      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 43,911 20,436  
United States Treasury Bills      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 36,881 16,738  
United States Government-Related Debt Securities      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 6,021 7,010  
Corporate Bonds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 1,003 1,351  
Basis of Fair Value Measurements, Level 1      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 27,080 79,970  
Basis of Fair Value Measurements, Level 1 | Money Market Funds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 27,080 79,970  
Basis of Fair Value Measurements, Level 1 | Commercial Paper      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 1 | United States Treasury Bills      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 1 | United States Government-Related Debt Securities      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 1 | Corporate Bonds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 2      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 87,816 45,535  
Basis of Fair Value Measurements, Level 2 | Money Market Funds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 2 | Commercial Paper      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 43,911 20,436  
Basis of Fair Value Measurements, Level 2 | United States Treasury Bills      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 36,881 16,738  
Basis of Fair Value Measurements, Level 2 | United States Government-Related Debt Securities      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 6,021 7,010  
Basis of Fair Value Measurements, Level 2 | Corporate Bonds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 1,003 1,351  
Basis of Fair Value Measurements, Level 3      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 3 | Money Market Funds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 3 | Commercial Paper      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 3 | United States Treasury Bills      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 3 | United States Government-Related Debt Securities      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 0 0  
Basis of Fair Value Measurements, Level 3 | Corporate Bonds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities $ 0 $ 0